Combination catalytic and thermal cracking



May 23, 1944'.

J .,M. BARRON COMBINATION CATALYTIC AND THERMAL CRACKING Filed July 2, 1945 w mm ' Patented May 23, 1944 UNrrEo STATES PA'rsNjr orsi-ca I corrB-rNA'rroN egrlg AND 'rammar- Y' Joseph 4Mason Barron,

or to The Texas Company, New corporation of Delaware am Arthur, rex., .ulm-

York. N. Y., a

Application 'my z, ma, serial No. mazos 4 claims. (crise-4a) This invention relates to certain improvements in combination catalytic and thermal cracking of hydrocarbons for the production of gasoline or motor fuel.

The invention contemplates a process wherein hydrocarbon oil is subjected to thermal cracking in a reaction zone in which liquid and vapors are in countercurrent contact at cracking temperature, in .which the separated vapors from the thermal reaction zone are subjected to fractionation to separate higher boiling from lower boiling fractions and in which the higher boiling fractions are recycled to the thermal cracking zone while lower boiling or intermediate boiling fractions are subjected to catalytic cracking. In accordance with the invention a condensate stock is passed through a heating zone and subbe converted to coke autogenously by mere dashing. vapors from the coking operation are dephlegmated with a. petroleum residual stock such as topped or reduced 'crude and the bottoms jected to a cracking temperature. The heated eiiluent is directed to the lower portion of a vertically disposed reaction chamber while a high boiling or residual stock is introduced into the upper portion of the reaction chamber to ilow countercurrently to the upwardly rising vapors. The dephlegmation of the vapors undergoing cracking in the countercurrent cracking chamber functions to prevent the delivery to the subsequent fractionator of certain heavy potential carbon-forming polymers with the result that the high boiling reflux condensate produced in the subsequent fractionator is adapted for recycling to a thermal cracking zone even when subjected to very high rates of cracking per pass therein. It is found that the high boiling fraction separated from the vapors may have a suiciently low color and carbon residue that it may be subjected to such high rates of cracking per pass without encountering coking difficulties as to effect conversion into high antimock gasoline constituents. Lighter fractions obtained from the fracitionating zone may be ,passed directly as a vapor to the catalytic cracking zone or such lighter fractions may be subjected to additional fractionation so as to recover the thermally cracked gasoline in which case the intermediate boiling fractions are passed to the catalytic cracking zone. Since high antimock gasoline is produced in the catalytic cracking zone, the overall result of the combined steps is the production of a maximum yield of high anti-knock gasoline.

The counteriiow operation in the thermal cracking chamber enables the maintenance of a sufiiciently high cracking temperature therein that the residue from the cracking chamber may produced in the dephlegmation are introduced into the upper portion of the thermal reaction chamber for thermal cracking under conditions of countercurrgnt flow; Awhile the lighter fractions are combined directly with the oil passing to the thermal cracking zone or are reuxed in the fractionating zone in which the thermally cracked vapors are fractionated. Products from the catalytic cracking are likewise combined with the vapors from the coking operation for fractionation therein so that the higher boiling fractions may be directed to the thermal cracking Zone.

The invention will be more clearly understood from the following description and from the accompanying diagrammatic drawing or ow diagram which illustrates the preferred apparatus or system-for practicing my combination catalytic and thermal cracking process.

Condensate stock is heated to a cracking temperature and subjected to vaporization and cracking in a heating coil Il disposed in a furnace Il. The heated eilluent passes through a transfer line I2 to a reaction chamber i3. As illustrated the transfer line extends within the lower portion or the reaction chamber and terminates'in an enlarged pipe or section it through which the heated productsl are discharged in an upward direction against a baiiie I5. In practice with a three-inch transfer line the element Il maybe composed of a six-inch pipe. The products passing from the coil lliv to the reaction chamber I3 will consist largely or entirely of vapors and gases and upon being discharged through the enlarged pipe I4 against the baiiie I 5v an emcient diffusion of the vapors and gases is accomplished. A black oil or residual stock is introduced to an upper portion of the reaction chamber through a line I6 which extends within the reaction chamber and terminates in a distributor or spray nozzle l1. The spray l1 is arranged to spray the liquid oil in aI downward direction through the chamber so as to bring the liquid into intimate contact with the rising vapors. It is desirable to have an unobstructed space between the distributor l5 and spray nozzle l1 free from' baiiies or any other contact elements upon which coke deposition might occur.

Separation of vapors from' liquid residue takes place in the reaction chamber I3. The separated vapors pass through a vapor line I8 to a fractionator I9 wherein the vapors'are subjected to fractionation to separate a high boiling fraction, which collects at the bottom of the fractionator and an intermediate boiling fraction, which collects in a tray 20, while uncondensed vapors pass to a condenser 2I and a. distillate receiver or gas separator 22 wherein the distillate is collected.-

The higher boiling reflux condensate is withdrawn through a line 23 and directed by a pump 24 through a line 25 to the heating coil I0.

The intermediate fraction is withdrawn from tray 20 through a line 26 and is directed by a pump 21 to a heating coil 28 disposed in a furnace 29 wherein the condensate is vaporized and heated to the temperature desired for catalytic cracking. The heated eiluent passes to a catalytic cracking zone 30 wherein it is contacted with a catalyst adapted to catalyze a conversion into lower boiling products.

The catalystconsists advantageously of a synthetic silica-alumina type of catalyst. Various acid-treated and metal-substituted clays such as the Super-Filtrols `and acid-treated and metalsubstituted natural or artificial zeolites, such as the artificial zeolite known as Doucil may be employed. Variousmetals such as uranium, molybdenum, manganese, lead? zinc, zirconium,- nickel and the like, may be substituted in the clays or zeolites. acid-treated active clays of the character of Filtrol, together with added proportions of alumina or silica or both may be employed. Alumina alone may be used under certain conditions. The synthetic alumina catalysts can be improved by the addition of other constituents such as zirconium oxide or molybdenum oxide. The catalyst may be provided as a stationary bed through which the vapors pass, or the vapors may pass over a continuously moving mass of granular catalyst, or the catalyst in a finely divided, comminuted or powdered form may be suspended in the vapors being introduced into the reaction chamber, or suspended in a gaseous medium whereby the catalyst is carried along with the vapors through the reaction'zone. In the fixed bed method of catalytic cracking a plurality of catalyst chambers may be used so that the catalyst may be regenerated without interrupting the continuity of the complete process, and in the case of the moving catalyst, the catalyst may be removed from the contacting reaction zone to a regenerating zone.

The products of the catalytic cracking pass through a transfer line 3I to a fractionator 32 wherein the products are fractionated to recover the catalytic gasoline which is removed as a vapor to a condenser 33 and collected as a distillate in an-accumulating drum or gas separator 34 while the higher boiling productsare withdrawn through a line 35.

Referring again to the thermal cracking step, liquid is prevented from accumulating in the reaction chamber I3 by the rapid withdrawal of liquid residue therefrom. The residue is passed through a line 36 and pressure-reducing valve 31 to a coking drum 38 wherein the liquid is converted to coke by means of its contained' heat. In practice a plurality of coking drums are employed so as not to interrupt the continuity of the complete process for the purpose of coke removal. The coking drums are' suitably heat-insulated. In practice a very slight amount of vapor may be included with the liquid withdrawn from the reaction chamber I3, an amount merely su'flicient to insure that no liquid level is maintained therein.

Likewise, the combination of certain However, by reason of the countercurrent contacting in the reaction chamber and by the avoidance of the accumulation of liquid therein a sumeiently high temperature can be maintained in 5 the reaction chamber that the withdrawn residue may be ash'ed to coke solely by means of its contained heat.

The vapors from the coking drum pass through a vapor line 39 to a fractionator 40, the vapors l0 preferably entering a primary dephlegmating zone 4I below a trap-out tray 42 wherein they are subjected to dephlegmation to separate out the polymer or synthetic fuel oil which is removed through a line 43. The dephlegmated vapors are subjectedto further dephlegmation and fractionation in the tower 40 above the tray 42 to separate a high boiling fraction which is collected in the tray 42. Uncondensed vapors pass to a condenser 44 and the condensate is collected in an accumulator or gas separator 45. The distillate from the drum 45 may be directed by a pump 46 through a. line 41 to the fractionator-I'S for refractionation therein.v

The higher boiling products from the catalytic 5 cracking operation, as withdrawn through line 35, maybe directed by a pump 43 through a line 43 to the fractionator 40, being preferably introduced above the tray 42. If desired, the separate fractionating step conducted in the tower 32 may be omitted and the entire products from the catalytic cracking operation passed directly from the line 3l to the fractionator 40 for a fractionation therein together with the vapors from the coking op eration. It is generally preferable however to subject the products from the catalytic cracking step to a separate fractionation in order to separately recover the catalytic gasoline before combining with the coke still vapors for further fractionation.

Charging stock, such as crude petroleum or topped crude, is introduced by a pump 59 through a line 5I and heat exchanger 52 wherein the charging stock is heated to a desired distilling temperature as by' contact with hot products from the thermal or catalytic cracking.' operation. The heated charging stock is separated into vapors and residue in a flash tower or fractionatcr53 from which residue is withdrawn by a pump 54 and directed to the fractionator 4l. The separated vapors in the'tower 53 are sub- "O- .iected to fractionation to obtain a reflux condensate collected in the tray 55 while uncondensed vapors pas's to a condenser 56 and the distillate is collected in an accumulating drum 51. Reflux condensate from tray 55 is directed 05 through a line 58 to the line 26 for introduction together with the condensate from tray 20 to the cata-lytic crackingr step. Thus the crude charge is fractionated to obtain a condensate such as gas oil, which is sent to the catalytic cracking step,l and a residue which serves to dephlegmate the vapors from the comng operation. The resultant mixture of condensate and unvaporized charging stock-is withdrawn from the tray 42 by a pump 59 and directed by a line El! through line I6to constitute the higher boiling stock which is introduced to the upper portion of the thermal cracking chamber- I3. The products fromv the catalytic cracking operation are likewise subjected to fractionation in the tower di). The overhead distillate which is collected in the receiver 45 consists of light products, such as gasoline, produced in the coking operation and intermediate boiling range products of the nature of kerosene and gas oil. The refractonation of assaeos the gasoline from the coking operation with the gasoline from the thermal cracking step and to combine constituents of intermediate boiling range recovered from the coking and catalytic cracking operations with constituentsof similar boiling range obtained from the thermal cracking step, for passage to the catalytic cracking step. Y

In an alternative method of operation an adduona1 fraction is withdrawn from the tower l from a tray BI and is combined by a pump 62 with the reux condensate passing through line 23 from the tower I9 to be thereby sent.to the heating coil I0. In this method of operation a gasoline fraction is taken overhead from the tower 40 and collected in the drum I5 and this gasoline distillate may be reuxed in the tower l@ or withdrawn from the system; while an intermediate boiling or gas oil fraction is collected on the tray 6l for passage to the thermal cracking zone; This method has the advantage of subjecting the catalytic `gas oil to a thermal cracking operation prior to again. subiecting it to catalytic cracking. The thernal treatment serves to recondtion the stock and make it better suited for catalytic cracking.

When it is not desired to reduce the bottoms from reaction chamber I3 to coke, the coke drum may be by-passed and the residual constituents` withdrawn from the reaction chamber I3, passed through a line 63 directly to the evaporating zone l and subjected to hashing to separate a liquid residue, withdrawn through line I3, from vapors winch are dephlegmated and fractionated in a manner similar to that described for the treatment of the vapors from the coking operation.

In practicing the invention cracking temperatures upwards of 900 F. under superatmospheric pressure such as 200-600 lbs. are maintained in the thermal reaction chamber I3 wherein the black oil is in countercurrent contact with the upwardly rising vapors. Liquid is prevented from accumulating by rapidly withdrawing the liquid residue with the result that conversion to coke is postponed until ,the residue reaches the coking drum 38. The vapors from the thermal' cracking operation are fractionated in the fractionator I9 to obtain gasoline, light gas oil and heavy gas cil fractions'. The heavy gas oil, withdrawn through line 23, by reason of its relatively low carbon residue may be subjected to relatively high rates of cracking per pass without coking. This gas oil stock is combined with reflux condensate obtained from the coking operation, withdrawn from the tray 6| of the tower 40. The fraction withdrawn from the tray 6| may advantageously be of lower endpoint than that of the heavy fraction withdrawn from the bottom of the tower I9. Thus in practice the bottoms from tower I9 may include heavy hydrocarbons boiling above '150 F. (as determined by a vacuum distillation and interpolated to an atmospheric pressure basis) while the stock withdrawn from tray 6I may have an endpoint of 600-700" F. and may consist largely of kerosene and light gas oil constituents. The composite stock directed to the heating coil I0 is subjected to cracking temperatures of 'the order of 1000 F. therein. The crude residue withdrawn from the tower 53 and the catalytic bottoms from the iractionator 32 serve to dephlegmate the vapors from the coking operation and are subjected to refractionation in contact with such vapors. The heavy fraction, withdrawn from the tray 42, includes the residual component of the .-crude as well as heavy gas oil constituents and this fraction, with or without such preheating as may be ldesired, is sprayed intothe top of the thermal cracking chamber. The charge to the catalytic cracking step is composed of alight gas oil or kerosene fraction collected -in the tray 29 of th'efractonator I9 and of straight-run gas \oil or kerosene fractions-obtained in the fraction--` ation of the crude.' It is advantageous to obtain in the crude fractionation a relatively wide boiling rangevgas oil cut having-a relatively high endpoint; while the fraction fromtray 2l is of a much lower endpoint. The composite charge is heated to temperatures of the order of 900- 1000Au F. in the heating coil 28 and contacted with a catalyst such as synthetic composite comprising precipitated silica and alumina and subjected to catalytic cracking.

Although a preferred embodiment of the invention has been described herein, it will be understood that various changes and modifications may be made therein, while securing to a greater or less extent some or all of the benefits of the invention, without departing from the spirit and scope thereof.

I claim:

1. In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises passing hydrocarbon oil through a heating zone wherein it is heated to a cracking temperature and subjected to thermal cracking, introducingthe resultant heated products to the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual stock to the upper portion of the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamber'to effect thermal cracking, withdrawing the liquid residue and subjecting it to coking, subjecting the separated vapors to fractionation in a fractionating zone to separate lower4 boiling fractions from higher boiling fractions, recycling said higher boiling fractions to said heating zone, `withdrawing said lower boiling fractions from the fractionating zone and combining them with a straight-run condensate stock, subjecting the mixture to catalytic cracking, combining resultant products from the catalytic cracking operation and a petroleum residual stock with vapors from the coking operation and subjecting the admixed constituents to fractionation to obtain a 'condensate fraction and a residual fraction, utilizing said residual fraction as the stock introduced to the upper portion of the vertically disposed reaction chamber, and directing the condensate fraction to the aforesaid fractionating zone for refractionation therein.

2. In the combination thermal and catalytic' cracking of hydrocarbon oils the process that comprises passing hydrocarbon oil thrgugh a heating zone wherein it is heated to a cracking' temperature and subjected to thermal cracking, introducing the resultant heated products to the lowe: lportion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual stock to the upper portion of the vertically disposed reaction chamber to iiow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamber to effect thermal cracking, withdrawing the liquid residue and flashing it to coke, subjecting the separated vapors from the reaction tionation to obtain a condensate fraction and a residual fraction, utilizing said residual fraction as the stock introduced to the upper portion of the vertically disposed reaction chamber, and directing the condensaterfraction to the aforesaid fractionating zone for refractionation therein.

3. In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises passing hydrocarbon oil through a heating zone wherein it is heated to a cracking temperature and subjected to thermal cracking, introducing the resultant heated products to the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual stock-to the upper portion of the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamberto effect thermal cracking, withdrawing the liquid residue and flashing it to coke, subjecting the separated vapors from the reaction chamber to fractionation in a fractionating zone to separate` lower boiling fractions from higher boiling fractions, recycling said higher boiling fractions to said heating zone, withdrawing said lower boiling fractions from the fractionating zone and combining them with a straight-run condensate stock, subjecting the mixture to catalytic cracking, fractionating the resultant catalytically cracked products to separate 'gasoline from higher boiling products, contacting vapors from the coking operation with said higher boiling products and with a petroleum residual stock and subjecting the admixed constituents to fractionation to obtain a condensate fraction and a residual fraction, utilizing said residual fraction as the stock introduced to the upper portion of the vertically ldisposed reaction chamber, and combining the condensate fraction with the aforesaid higher boiling fractions being recycled to the said heating zone.

4. In the combination thermal and catalytic cracking of hydrocarbon oils the process that comprises passing 'hydrocarbon oil through a heating zone wherein it is heated to a cracking temperature and subjected to thermal cracking, introducing the resultant heated products to the lower portion of a vertically disposed reaction chamber wherein separation of vapors from liquid residue takes place, introducing a residual stock to the upper portion oi the vertically disposed reaction chamber to flow countercurrently to the upwardly rising vapors therein, maintaining a cracking temperature in said reaction chamber to effect thermal cracking, withdrawing the liquid residue and flashing it to coke, subjecting the separated vapors from the reaction chamber tol fractionation in a fractionating zone to obtain a lower boiling fraction, an intermediate boiling fraction and a higher boiling fraction, recycling the higher boiling fraction to said heating zone, disti1ling crude petroleum to obtain a gas oil fraction and a residual fraction, combining said intermediate boiling fraction with the gas oil fraction from the crude and subjecting the mixture to catalytic cracking; fractionating the resultant catalytically cracked products to separate gasoline from higher boiling products, contacting vapors from the coking operationwith said higher boiling products and with said residual fraction from the crude petroleum and subjecting the admixed constituents to fractionation to obtain a condensate fraction and a residual fraction, utilizing the latter residual fraction as the stock introduced to the upper portion of the vertically disposed reaction chamber, and combining the condensate fraction with the aforesaid higher boiling fractions being recycled to the said heating zone.

JOSEPH MASON BARRON. 

